Production of alloy steel



Patented May 8, 1945' PRODUCTION OF ALLOY STEEL Ernest F. Doom, New Rochelle, N. Y., assignor to :Electro Metallurgical Company, a corporation -of West Virginia No prawin Application April 3, 1941, Serial No. 386,659

4Claims. (01. 75-1305 The invention relates to the production of chromium-containing alloy steels, and has for its principal object improvements in the addi tion of chromium to a steel bath.

In manufacturing chromium steels by the process most commonly used, a bath of molten steel is prepared, and chromium is added to the bath in the form of ferrochromium. The principal demand is for a ferrochromium contain-' ing 65% to 70% chromium, but alloys containing less chromium maybe, and are used. Ordinarily, the steel bath is prepared in an electric furnace, but if a chromium steel containing no more than about 3% chromium is to bemade,

the less expensive open hearth furnace method .is sometimes used. Adjustment of the chromium content. of steels may be made in the ladle after the steel is tapped from the furnace, but

solution in the steel bath. The melting point of ferrochromium is high, and large additions of the alloy have a chilling effect upon the bath. This chilling efiect tends to decrease the rate of For steels containing more than about chromium by oxidation and prevent good recov cry of chromium in the steel. Improvement is sought in the method of manufacture of chromium steels which would obviate these disadvan tages.

.The present invention, 'which provides improvements in this direction, is based on the discovery that a ferrochromium 'alloy which con-. tains substantial proportions of manganese and siliconis considerably more readily soluble in a molten ferrous meta-l bath than ferrochromiums of the ordinary composition. The invention accordingly comprises the addition to a molten steel bath of an alloy containing about 40% to 70%' chromium, 0.05% to 7% carbon and 3% to 20% in the aggregate of manganese and silicon, the remainder iron. Preferably, the manganese content is in excess of the silicon content. A presolution of the chromium in the bath. Also, even more importantly, there is formed on the surfaces of the addition a ent a coat'ng or sk n of refractory oxide, which materially retards the melting and solution of the addition agent. Be- 1 cause of these factors it is necessary, when large additions of chromium are to be made, to add itportionwise to the steel bath in the furnace. Thus, part of the ferrochromium is added and time is allowed for it to become molten and dissolved in the. bath before another addition 'is made. Frequently, part cularly in the manufacture of the higher chromium steels, the bath must be reheated between ferrochromium additions, and quite often the ferrochromium is preheated before it is added.

These facts tend to increase the cost of chromium steels because the increased time necessary to manufacture the steels and the lengthy heating periods made necessary promote the loss of ferred alloy for use according to the invention contains about 55% to 70% chromium, 5% to 15% manganese, 1% to 10% silicon, 0,05% to 7% carbon, the remainder iron.

It has been foundthat the surface of the crushed or otherwise conventionally comminuted solid'alloys justed described is such as to permit ready melting and solution in a ferrous metal bath. For instance, any coating formed on such alloys when added to a molten steel bath does not materially retard the solution or melting of the alloys. The lower melting point of such alloys is also an advantage.

When chromium is added to a molten steel bath by the use of a ferrochromium containing manganese and silicon in the ranges stated, the time required for the addition alloy to dissolve in the bath is substantially less than the time requiredfor solution of an ordinary ferrochromium. This decrease in solution time results in enhanced recovery of chromium, and using such an alloy it is possible to dissolve more chromium in the molten bath, before the bath cools to a point where more chromium will not dissolve, than can be dissolved when standard ferrochromium is used. The invent on therefore makes possible the production of much higher chromium steels in the open hearth furnace and permits the addition of two or three times as much chromium in. the ladle as can be added "in the present practice. Itis particularly well suited to use in the manufacture of steels containing about 0.75% to 5% or 6% chromium in the open hearth furnace, and probably will flnd its greatest ap plication in the manufacture of steels'containing about 2% to 4% chromium in the open hearth furnace. However, it is also useful in the manufacture of high chromium steels since it decreases the reheating necessary when the chromium is added to molten steel in the open.

hearth or electriciumace. Upwards of 1% chromium may be added to a ferrous metal bath without reheating in the practice of the invention.

In tests of the invention, steels of different chromium contents were produced to which the chromium was added by diflerent agents. In one such test a steel containing about 3.5% chromium, 0.10% carbon, 1% manganese and 0.4% silicon was produced. Three heats having this composition were melted in a basic lined high frequency furnace'under the same melting conditions. After the steel bath had been prepared, in each case an addition agent was added to the bath in the furnace in small, uniformly sized lumps. composition of the addition agent used in each heat, the time for the agent to dissolve completely in the bath, and the amounts of addition agent and chromium added to each heat.

Because of the difl'erences in chromium content of the addition agents used in the above tests, a greater weight of addition alloy wa required for the second and third heats than was i required for the first heat to obtain a steel of the desired analysis. Thus, in heat 1, 7.9 parts of addition agent were required, whereas, in heats 2 and 3, 8.98 and 9.65 parts of addition agent respectively were required. Despite the greater weight added in heats 2 and 3, the time for solution was less than that required for heat I. Thus, it is shown by Table I that an important increase in solution rate is obtained when a ferrov chromium containing" substantial proportions of manganese and silicon is used. c

In another test of the invention a steel containing 1.5% chromium, 0.75% manganese, 0.25% silicon and 0.40% carbon was made by preparing a steel bath in a basic lined furnace, tapping the heat into three ladies, and adding to each ladle, 1.5% chromium by means of different alloys. Again, quicker solution was obtained when ferrochromiums containing substantial proportions of manganese and silicon were used. Table II below sets forth the composition of the agents used, the time for complete solution of the agents in the ladies, and the temperature of the steel when tapped into the ladies. In each case, the addition agent was added to the stream flowing into the ladle.

In the following table are set forth the tion of chromium to a molten steel bath due to the increased solution rate of chromium. This improvement results in economy of time and power. Even more important, the recovery of chromium in the method of the-invention is substantially providing another advantage.

While the invention i particularly adapted to the manufacture of chromium steels in th open hearth furnace or by the addition of chromium in the ladle, it may be used to advantage in the production of higher chromium steels in the electric furnace.

I claim:

1. In the method of manufacturing chromium steels by preparing a bath of molten steel and adding chromium to the bath so prepared, the improvement which comprises adding the chromium as a. comminuted solid alloy containing 40% to 70% chromium, 0.05% to 7% carbon, at least 2% manganese and at least 1% silicon, the sum of the manganese and silicon percentages being between 3% and20%, the remainder iron.

2. In the method of manufacturing chromiumsteels which comprises preparing a bath of molten steel in an open hearth furnace and adding chromium to the molten bath so prepared, the improvement which comprises adding the chromium as a comminuted solid alloy containing 55% to 70% chromium, 0.05% to 7% carbon,

at least 2% manganese and at least 1% silicon,

the sum of the silicon and manganese percent- ?rges being between 3% and 20%, the remainder on. i

3. In the method of manufacturing chromium steels, which comprises preparing a bath of molten steel in an open hearth furnace and adding chromium to the molten bath so prepared, the improvement which comprises adding the. chromium as an alloy containing.55% to 70% chromium, 0.05% to 7% carbon, 5% to 15% manganese, 1% to 10% silicon, remainder iron, the sum of the silicon and manganese percentages being not more than 20%,

4. In the method of manufacturing chromium steel which comprises preparing a bath of molten steel in an open hearth furnace and adding chromium to the molten bath so prepared, the improvement which comprises adding about 0.75%;to 6% chromium to the bath as an alloy containing 55% to 70% chromium, 0.05% to 7% carbon, 5% to 15% manganese, 1% to 10% silicon, remainder iron, the sum of the silicon and gioazganese percentages being not more than ERNEST F. DOOM. 

